Method for applying semi-dry electroplating method on surface of plastic substrate

ABSTRACT

A method for applying a semi-dry electroplating method on a surface of plastic substrate is related to an electroplating method of plastic. which realizes the surface metallization of plastic materials, simplifies the electroplating procedure, dramatically reduces the amount of waste water, reduces the pollution to environment and expands electroplatable range of plastic substrates, is provided. Water-free cleaning and dust removal are conducted to a plastic substrate; a first-time activated treatment is conducted to the surface of the plastic substrate; a PVD plating metallic base layer, an alloy transition layer and a metallic electrical conductive layer are applied in turn on it, ultrasonic water washing and a second-time activated treatment are conducted on the treated plastic substrate; the treated plastic substrate is directly electroplated with acid copper or is moved to a nickel plating bath, and then complete the final surface treatment according to the actual process requirements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to an electroplating method, and moreparticularly to a method for applying a semi-dry electroplating methodon a surface of plastic substrate.

2. Description of Related Art

Since applying metalizing electroplating procedure on a surface of aplastic substrate can achieve anti-corrosive, wear-resisting,scratch-resisting effects and a decoration function with beautifulappearance, the application scope of the plastic substrate thus expands.However, such traditional plastic electroplating procedure has twodisadvantages including: (1) electroplatable plastic substrates beinglimited to ABS, PC/ABS and very few kinds of nylon; (2) pretreatmentbefore electroplating procedure (including each procedure of chemicaldegreasing and cleaning, roughening, naturalization, sensitization,chemical nickel-plating and so forth) resulting in a large amount ofdischarging waste water, which is not environmental friendly. Therefore,developing a novel green electroplating procedure with reduced dischargeis required. Simultaneously, a novel electroplating procedure, whichallows all kinds of plastic to conduct metalizing electroplating is moredesired. In this way, more economical benefits can be gained whilepollution to environment can be reduced.

For expanding application scope of electroplatable plastic, conventionalmethods are mainly included as follows:

1) Chinese Patent, CN03104647.9, discloses a method for sprayingelectrically conductive medium on plastic pieces and cooperatingelectrolytic plating to conduct electroplating of a plastic surface.

2) Chinese Patent, CN02127419.3, used a method for roughening withdichromic acid content and activation of noble metal to metalizedifferent kinds of plastics.

3) Chinese Patent, CN200410018367.2, used a vacuum sputtering method,which form a thin layer of basic metallic coating by sputtering on asurface of non-metallic material to conduct metallization.

The insufficiency of the foregoing methods 1) and 2) is that usingdichromic acid and spraying electrically conductive paint result inserious environmental pollution problem and has higher cost ofproduction. Using metallization technology with vacuum evaporationcoating on a plastic substrate is more environmentally friendly whencompared to the foregoing methods 1) and 2). However, such simple way ofvacuum evaporation coating leads to poor adhesion between the plasticsubstrate and PVD metallic layer. After electroplating, abscissionlayer, foaming or other phenomena would occur between the plasticsubstrate and PVD metallic layer or the final electroplating productsconfront failure in the thermal cycling test or other problems.

SUMMARY OF THE INVENTION

The objective of the present invention is, in view of disadvantages andinsufficiency existing in the conventional plastic electroplatingprocedure, to provide a method for applying a semi-dry electroplatingmethod on a surface of a plastic substrate, which realizes surfacemetallization of plastic materials, simplifies an electroplatingprocedure, dramatically reduces the amount of waste water, reduces thepollution to environment and expands electroplatable range of a plasticsubstrate.

The present invention includes the following steps:

1) conducting water-free cleaning and dust removal to a plasticsubstrate;

2) conducting a first-time activated treatment to the surface of theplastic substrate;

3) applying a PVD plating metallic base layer, an alloy transition layerand a metallic electrical conductive layer in turn on theactivated-treated surface of the plastic substrate;

4) conducting an ultrasonic water washing and a second-time activatedtreatment on the plastic substrate treated in the step 3);

5) directly electroplating the plastic substrate treated in the step 4)with acid copper or moving it to a nickel plating bath to conduct nickelelectroplating;

6) moving the plastic substrate treated in the step 5) into a chromiumplating bath to conduct a final chromium electroplating or transferringit to a PVD oven to conduct deposition of chromium layer.

In the step 1), said plastic substrate can use a plastic substrateproduced by injection molding or extrusion molding. Said plasticsubstrate can use engineering-plastics, glass fibers or mineral-powderreinforcing plastics or the like. Said engineering-plastics can beselected from one of ABS, PC, PC/ABS blends, PA6, PETG, PBT, PA66, TPU,TPU/ABS blends or the like. Said glass fiber reinforcing plastics can beselected from one of PA6+glass fiber, PBT+glass fiber, PC+glass fiber,PA66+glass fiber, PP+glass fiber or the like. Said mineral-powderreinforcing plastics can be selected from one of PA6+mineral powder,PP+mineral powder or the like. Said water-free cleaning can use thefollowing methods: First, Electrostatic precipitation of the productsurface, then wipe the surface of the product with anhydrous alcohol,And then using ion-source glow cleaning or bias glow cleaning in a PVDoven or corona activated treatment, washing with water first to removeoil then drying if the product surface is severely contaminated withgreasy dirt, And then using ion-source glow cleaning or bias glowcleaning in a PVD oven or corona activated treatment.

2) conducting a first-time activated treatment to the surface of theplastic substrate:

In the step 2), said first-time activated treatment can use followingmethods: plasma glow modification using ion-source glow or bias glowmode to conduct the activated treatment, or corona activated treatment.

In the step 3), said metallic base layer can be a metallic base layer oran alloy base layer using chromium, titanium, aluminum, nickel, iron,zirconium or the like. Said metallic base layer can use arc ion platingor magnetron sputter plating to produce the PVD base layer. Said alloytransition layer is an alloy layer with at least one metal selected fromchromium, titanium, aluminum, nickel, iron, zirconium, copper or thelike and can be produced by arc ion plating or magnetron sputterplating. Said metallic electrically conductive layer can be a metallicelectrically conductive layer of copper, nickel or other metal. Saidmetallic electrically conductive layer can use arc ion plating ormagnetron sputter plating to produce the PVD base layer.

In the step 4), said ultrasonic water washing comprises transferring theplastic substrate treated in the step 3) into water galvanization lineto conduct the ultrasonic water washing. Activating solution used insaid second-time activated treatment can use sulfuric acid solution orthe like.

In the step 5), if the surface of the plastic substrate is not flat,electroplating starts from plating acid copper. Said nickelelectroplating can use at least one of semi-bright nickel, fully-brightnickel, microporous nickel or the like. If the surface of the plasticsubstrate is flat, electroplating directly starts from electroplating asemi-bright nickel layer, then electroplating a fully-bright nickellayer or a microporous nickel layer or the like.

Since plastics used in conventional electroplating procedure are limitedto ABS, PC/ABS and very few PA6, glass fiber reinforced PBT or glassfiber reinforced PC or the like, the electroplating of plastic surfacessuffers from a tremendous limitation. The present invention usesimproved PVD surface plating technology to treat the surface of thesubstrate with the water-free clean, the activated treatment and PVDmultilayer technology, to plate the electrically conductive layer on theplastic surface first with physical vapor deposition (PVD), then totransfer the plastic substrate into traditional electroplating procedureto metalize the surface of the plastic material, and to incorporatesimplified electroplating to prepare a semi-dry electroplated productwith high quality. Pretreatment before electroplating is not requiredand therefore traditional chemical degreasing, roughening,naturalization, sensitization, chemical nickel-plating and so forth canbe ignored. The procedures of electroplating the copper layer,electroplating the nickel layer and electroplating the chromium layerare directly conducted or electroplating chromium can be conducted in aPVD stove. As a result, the semi-dry electroplated product with highquality can be produced. Additionally, the amount of wastewaterdischarge in the present invention is merely a half of that in thetraditional electroplating procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, as well as its many advantages, may be further understoodby the following detailed description and drawings in which:

FIG. 1 is a cross-sectional side view of the product prepared by example1 of the present invention. In FIG. 1, from the bottom to the top, thereare a plastic substrate, a vacuum vapor deposited layer (PVDCr/CrCu/Cu), an electroplated acid copper layer, an electroplatedsemi-bright nickel layer, an electroplated fully-bright nickel, anelectroplated microporous nickel layer, and a electroplated brightchromium layer.

DETAILED DESCRIPTION OF THE INVENTION Example 1 Procedure of Semi-DryElectroplating Method when the Surface of a Plastic Piece is Flat

Applying semi-dry electroplating method on a surface of a car-doorhandle with PC+ABS plastic substrate has following specific steps:

Step 1 (injection molding): PC+ABS engineering plastic resin was driedat 80° C. for 4 h, and then was injection molded to form a plastic pieceof car-door handle. The surface of plastic piece was flat.

Step 2 (cleaning of plastic piece and plasma surface modification): Thecleaning (dry cleaning) procedure before plating comprises wiping thesurface with anhydrous alcohol and plasma glow cleaning in a PVD stove.Parameters for the plasma glow cleaning comprise: Ar flux being 65 sccm,time for glow cleaning being 5 min, bias voltage being 70V, bias vacuumratio being 70%, and ion source current being 0.3 A.

The plastic piece after cleaning was put into a vacuum oven to conductplasma surface modification. Parameters for the plasma glow surfacemodification comprise: O₂ 100 sccm, ion source current being 0.3 A, timefor surface modification being 10 min, bias voltage being 70V, and biasvacuum ratio being 70%.

Step 3 (PVD metallic base layer and alloy transition layer): For PVDmetallic base layer, the target was metallic Cr target and arc ionplating was used for plating. Ar flux was 50 sccm, Cr target current was50 A, bias voltage was 60V, bias vacuum ratio was 75%, time for platingwas 5 min, and vacuum pressure for plating was 0.13 Pa. The alloytransition layer was CrCu alloy transition layer using arc Cr target andsputtering Cu target to form a CrCu alloy membrane with arc Cr targetcurrent being 50 A, copper target current for magnetron sputter platingfrom 2 A gradually raised to 8 A, bias voltage being 60V, bias vacuumratio being 75%, time for plating being 8 min, Ar flux being 130 sccm,and vacuum pressure for plating being 0.3 Pa.

Step 4 (PVD electrically conductive layer): A magnetic sputter platingcopper target was used for plating with copper target current being 8 A,bias voltage being 70V, bias vacuum ratio being 70%, time for platingbeing 40 min, Ar gas flux being 130 sccm, and vacuum pressure forplating being 0.3 Pa.

Step 5 (galvanic plating): The product was transferred to hang onplating racks and was started to be plated from water washing andactivation before contacting acid copper. Plated layers in turn compriseacid copper, semi-bright nickel, fully-bright nickel, microporousnickel, and bright chromium.

Example 2 Procedure of Semi-Dry Electroplating Method when the Surfaceof a Plastic Piece is not Flat

Applying semi-dry electroplating method on a surface of a faucet knobmade of polyamide modified engineering plastics has following specificsteps:

Step 1 (injection molding): Polyamide modified engineering plasticpowder was dried at 120° C. for 4 h, and then was injection molded toform a plastic piece of faucet knob. Since the ingredients formodification comprise glass fibers, the surface of plastic piece haslittle orange peel.

Step 2 (cleaning of plastic piece and plasma surface modification): Thecleaning (dry cleaning) procedure before plating comprises wiping thesurface with anhydrous alcohol and plasma glow cleaning in a PVD stove.Parameters for the plasma glow cleaning comprise: Ar gas flux being 65sccm, time for glow cleaning being 5 min, ion source current being 0.3A, bias voltage being 70V, bias vacuum ratio being 70%, and ion sourcecurrent being 0.3 A. If the surface of the product is contaminatedseverely, washing with water would be required to remove oil, time foroil-removal and water-washing is 5 min and then the surface of theproduct would be dried under 120° C.

The plastic piece after cleaning was put into a vacuum oven to conductplasma surface modification. Parameters for the plasma glow surfacemodification comprise: O₂ gas flux being 100 sccm, time for surfacemodification being 10 min, bias voltage being 70V, and bias vacuum ratiobeing 70%.

Step 3 (PVD metallic base layer and alloy transition layer): For PVDmetallic base layer, the target was metallic Cr target and physicalsputter plating was used for plating with Ar flux being 130 sccm, Crtarget current being 8 A, bias voltage being 60V, bias vacuum ratiobeing 75%, time for plating being 5 min, and vacuum pressure for platingbeing 0.29 Pa. The alloy transition layer was CrCu alloy transitionlayer using medium frequency magnetron sputter plating Cr target andmagnetron sputter plating Cu target to form a CrCu alloy membrane.Current of the medium frequency magnetron sputter plating Cr targetgradually decreased from 8 A to 0 A, copper target current for magnetronsputter plating gradually raised from 2 A gradually raised to 8 A, biasvoltage was 60V, bias vacuum ratio was 75%, time for plating was 8 min,Ar 130 sccm, and vacuum pressure for plating being 0.3 Pa.

Step 4 (PVD electrically conductive layer): A copper target was used anda magnetic sputter plating was used for plating with copper targetcurrent being 8 A, bias voltage being 60V, bias vacuum ratio being 75%,time for plating being 40 min, Ar 130 sccm, and vacuum pressure forplating being 0.3 Pa.

Step 5 (galvanic plating): The product was transferred to hang onplating racks and was started to be plated from water washing andactivation before contacting acid copper. Plated layers in turn compriseacid copper, semi-bright nickel, fully-bright nickel, microporousnickel, and bright chromium.

Example 3

Applying semi-dry electroplating method on a plastic substrate surfaceof a high-density ball head made of polyamide modified engineeringplastic has following specific steps

Step 1 (injection molding): Polyamide modified engineering plasticpowder was dried at 120° C. for 4 h, and then was injection molded toform a plastic piece of high-density ball head. The surface of theplastic piece was flat.

Step 2 (cleaning of plastic piece and surface modification): The driedplastic piece was put into a vacuum oven to conduct plasma glow cleaningand plasma surface modification. Parameters for the plasma glow cleaningcomprise: Ar gas flux being 65 sccm, time for glow cleaning being 5 min,ion source current being 0.3 A, bias voltage being 70V, bias vacuumratio being 70%, and ion source current being 0.3 A. Parameters for theplasma surface modification comprise: O₂ gas flux being 100 sccm, timefor gloss surface modification being 10 min, bias voltage being 70V, andbias vacuum ratio being 70%.

Step 3 (PVD metallic base layer and alloy transition layer): For PVDmetallic base layer, the target was Cr target and arc ion plating wasused for plating with Ar flux being 50 sccm, Cr target current being 50A, bias voltage being 60V, bias vacuum ratio being 75%, time for platingbeing 5 min, and vacuum pressure for plating being 0.13 Pa. The alloytransition layer was CrCu alloy transition layer using arc Cr target andsputtering Cu target to form a CrCu alloy membrane with arc Cr targetcurrent being 50 A, copper target current for magnetron sputter platingfrom 2 A gradually raised to 8 A, bias voltage being 60V, bias vacuumratio being 75%, time for plating being 8 min, Ar flux being 130 sccm,and vacuum pressure for plating being 0.3 Pa.

Step 4 (PVD electrically conductive layer): A copper target was used asthe target and a magnetic sputter plating was used for plating withcopper target current being 8 A, bias voltage being 60V, bias vacuumratio being 75%, time for plating being 40 min, Ar 130 sccm, and vacuumpressure for plating being 0.3 Pa.

Step 5 (galvanic plating): The product was transferred to hang onplating racks and was started to be plated from water washing andactivation before forming semi-bright nickel. Plated layers in turncomprise semi-bright nickel, fully-bright nickel, microporous nickel,and bright chromium.

The comparison of examples 1˜3 is shown in Table 1.

TABLE 1 Example 1 2 3 Plastic substrate ABS + PC PA6 + 30% GF + PA6 +iron iron powder powder plating types CP CP CP Product Car handle Coverof faucet Ball head Appearance of Flat Little orange peel Flat plasticpiece Surface cleaning Anhydrous Water washing and Plasma glow alcoholwipe oil removal cleaning Surface Plasma glow Plasma glow Plasma glowmodification modification modification modification Metallic base Arc CrSputtering Cr Arc Cr layer Alloy transition CrCu CrCu CrCuElectrically-conduc- Cu 1 μm Cu 1 μm Cu 1 μm   tive layer Acid copper15~20 μm 15~20 μm 0 μm Semi-bright nickel 6 μm 6 μm 6 μm Fully-bright 9μm 9 μm 9 μm nickel Microporous 1 μm 1 μm 1 μm nickel Bright chromium0.25 μm 0.25 μm 0.25 μm   Copper-accelerated pass pass pass aceticacid-salt spray corrosion test 8 h corrosion test Thermal cycling passpass pass

Many changes and modifications in the above described embodiment of theinvention can, of course, be carried out without departing from thescope thereof. Accordingly, to promote the progress in science and theuseful arts, the invention is disclosed and is intended to be limitedonly by the scope of the appended claims.

1. A method for applying semi-dry electroplating method on surface ofplastic substrate, characterized in that the method comprises followingsteps including: (a) conducting water-free cleaning and dust removal toa plastic substrate; (b) conducting a first-time activated treatment tothe surface of the plastic substrate; (c) applying a PVD platingmetallic base layer, an alloy transition layer and a metallic electricalconductive layer in turn on the activated-treated surface of the plasticsubstrate; (d) conducting ultrasonic water washing and a second-timeactivated treatment on the plastic substrate treated in the step (c);(e) directly electroplating the plastic substrate treated in the step(d) with acid copper or moving it to a nickel plating bath to conductnickel electroplating; (f) moving the plastic substrate treated in thestep (e) into a chromium plating bath to conduct final chromiumelectroplating or transferring it to a PVD oven to conduct deposition ofchromium layer.
 2. The method for applying semi-dry electroplatingmethod on surface of plastic substrate as claimed in claim 1,characterized in that in the step (a), said plastic substrate uses aplastic substrate produced by injection molding or extrusion molding;said plastic substrate uses engineering-plastics, glass fibers ormineral-powder reinforcing plastics; said engineering-plastics isselected from one of ABS, PC, PC/ABS, PA6, PETG, PBT, PA66, TPU,TPU/ABS; said glass fiber reinforcing plastics is selected from one ofPA6+glass fiber, PBT+glass fiber, PC+glass fiber, PA66+glass fiber,PP+glass fiber; said mineral-powder reinforcing plastics is selectedfrom one of PA6+mineral powder, PP+mineral powder.
 3. The method forapplying semi-dry electroplating method on surface of plastic substrateas claimed in claim 1, characterized in that in the step (a), saidwater-free cleaning uses the following methods: (a1) electrostaticcleaning, (a2) anhydrous alcohol wipe, (a3) a using ion-source glowcleaning or bias glow cleaning in a PVD oven, (a4) corona treatment,(a5) washing with water first to remove oil then drying if the productsurface is severely contaminated with greasy dirt.
 4. The method forapplying semi-dry electroplating method on surface of plastic substrateas claimed in claim 1, characterized in that in the step (b), saidfirst-time activated treatment uses following methods: (b1) plasma glowmodification using ion-source glow or bias glow mode to conduct theactivated treatment, (b2) corona activated treatment.
 5. The method forapplying semi-dry electroplating method on surface of plastic substrateas claimed in claim 1, characterized in that in the step (c), saidmetallic base layer is metallic base layer or alloy base layer usingchromium, titanium, aluminum, nickel, iron, zirconium.
 6. The method forapplying semi-dry electroplating method on surface of plastic substrateas claimed in claim 1, characterized in that in the step (c), saidmetallic base layer uses arc ion plating or magnetron sputter plating toproduce PVD base layer; said alloy transition layer is an alloy layerwith at least two metals selected from chromium, titanium, aluminum,nickel, iron, zirconium, copper and is produced by arc ion plating ormagnetron sputter plating.
 7. The method for applying semi-dryelectroplating method on surface of plastic substrate as claimed inclaim 1, characterized in that in that in the step (c), said metallicelectrically conductive layer is a metallic electrically conductivelayer of copper, nickel; said metallic electrically conductive layeruses arc ion plating or magnetron sputter plating to produce the PVDbase layer.
 8. The method for applying semi-dry electroplating method onsurface of plastic substrate as claimed in claim 1, characterized inthat in the step (d), said ultrasonic water washing comprisestransferring the plastic substrate treated in the step (c) into watergalvanization line to conduct the ultrasonic water washing.
 9. Themethod for applying semi-dry electroplating method on surface of plasticsubstrate as claimed in claim 1, characterized in that in the step (d),activating solution used in said second-time activated treatment usessulfuric acid solution.
 10. The method for applying semi-dryelectroplating method on surface of plastic substrate as claimed inclaim 1, characterized in that in the step (e), if the surface of theplastic substrate is not flat, electroplating starts from plating acidcopper; said nickel electroplating uses at least one of semi-brightnickel, fully-bright nickel, microporous nickel; and if the surface ofthe plastic substrate is flat, electroplating directly starts fromelectroplating a semi-bright nickel layer, then electroplating afully-bright nickel layer or a microporous nickel layer.